The present invention relates to a lithographic printing plate precursor, and particularly to a lithographic printing plate precursor requiring no development processing, excellent in sensitivity and scumming resistance, and able to take both the positive and negative forms. More particularly, the invention relates to a lithographic printing plate precursor which can directly make a plate by operating an infrared laser based on a digital signal.
Previously, methods for directly making printing plates from digitized image data with no interposition of lithographic films have variously been proposed. However, these methods are complicated in post-processing treatment processes after exposure, or necessitate the waste liquid treatment of post-processing treatment solutions. They are therefore not necessarily satisfactory.
On the other hand, in the recent platemaking and printing industry, the rationalization of platemaking work has been promoted. Accordingly, printing plate precursors not requiring such complicated development processing as described above and usable for printing as such after exposure have been desired.
As printing plate precursors coping with the above-mentioned demand, JP-A-11-84658 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationsxe2x80x9d) discloses positive lithographic printing plate precursors in which polymers having groups changing from hydrophobic to hydrophilic by heat, such as sulfonate groups and alkoxyalkyl ester groups, are cross-linked, and JP-A-7-1849 discloses negative lithographic printing plate precursors in which microcapsules containing hydrophobic compositions reactable with hydrophilic groups are dispersed in cross-linked hydrophilic layers.
In these lithographic printing plate precursors, image recording layers have cross-linked structures, so that image areas and non-image areas are formed by the surface polar conversion, not by the removal of corresponding areas of the image recording layers. Accordingly, these precursors are of the non-processing type requiring no development processing.
However, even in the above-mentioned lithographic printing plate precursors, the sensitivity desired is not fully compatible with the scumming resistance of the resulting printing plates.
An object of the invention is to overcome the prior-art disadvantages described above to provide a positive or negative lithographic printing plate precursor which can form an image at high sensitivity by heating or heat developed by light-heat conversion, requires no development processing after image writing, has good sensitivity and excellent printing durability, is significantly improved in scuffing resistance, and can directly make a plate by operating an infrared laser based on a digital signal.
As a result of intensive investigation, the present inventors have discovered that the above-mentioned object is attained by the following means, thus completing the invention.
That is to say, the invention is as follows:
(1) A lithographic printing plate precursor comprising a polymer compound having a functional group changeable in hydrophilicity by heat, acid or radiation and an under layer with which the polymer compound is combined, wherein the polymer compound is directly combined with a surface of the under layer by chemical bonding;
(2) A lithographic printing plate precursor comprising a polymer compound having a functional group changeable in hydrophilicity by heat, acid or radiation and an under layer with which the polymer compound is combined, wherein the polymer compound is a straight-chain polymer compound directly combined at an end of a polymer chain thereof with a surface of the under layer by chemical bonding, or the polymer compound comprises (i) a polymer backbone chemically combined with a surface of the under layer and (ii) a straight-chain polymer compound combined at an end of a polymer chain thereof with the polymer backbone and having a functional group changeable in hydrophilicity;
(3) A lithographic printing plate precursor comprising a support having provided thereon a photosensitive layer containing at least a photo acid generator and a polymer compound having a functional group changeable in hydrophilicity by acid, the polymer compound being directly chemically combined with a surface of the support;
(4) The lithographic printing plate precursor described in (3), wherein the polymer compound is a straight-chain polymer compound directly chemically combined at an end of a polymer chain thereof with the surface of the support, or the polymer compound comprises (i) a polymer backbone chemically combined with the surface of the support and (ii) a straight-chain polymer compound combined at an end of a polymer chain thereof with the polymer backbone and having a functional group changeable in hydrophilicity; and
(5) The lithographic printing plate precursor described in (3) or (4), wherein the polymer compound is a polymer compound comprising a side chain having a functional group changeable from hydrophobic to hydrophilic by acid.
In the lithographic printing plate precursors of the surface polar conversion type described in JP-A-11-84658 and JP-A-7-1849, also the water retention of the image recording layers is considered to be necessary for expressing the hydrophilicity with no scumming in printing. For that purpose, it has been considered that the polar conversion is required to take place not only on surfaces of the image recording layers, but also in the inside of the layers. In the above-mentioned precursors, therefore, larger energy is required for allowing the polar conversion to take place in the inside of the image recording layers, and the ordinary amount of image recording energy sometimes results in low sensitivity. Fox enhancing the sensitivity at the ordinary amount of image recording energy, it is conceivable that the image recording layers are decreased in thickness. However, in the above-mentioned conventional lithographic printing plate precursors, the thinned layers cause deterioration of the water retention, resulting in deterioration of the scumming resistance. It has been therefore impossible to express sufficient discrimination between the hydrophilicity and the lipophilicity. Further, the thinned layers have raised the problem that the printing durability is deteriorated.
In contrast, according to the lithographic printing plate precursors of the invention, the polymer compound having the functional group changeable in hydrophilicity by heat, acid or radiation (hereinafter also briefly referred to as the xe2x80x9cpolar conversion groupxe2x80x9d) is combined with the surface thereof, for example, at an end of the compound directly or through the polymer backbone. Accordingly, water is retained among a plurality of chains of the polar conversion group-containing polymer in non-image areas. As a result, it is conceivable that even the thinned layer can express the hydrophilicity with no scumming in printing. As described above, the lithographic printing plate precursor of the invention can efficiently express the hydrophilicity, so that an image recording layer thereof can be decreased in thickness, and also increased in sensitivity. Further, in the lithographic printing plate precursor of the invention, the polymer compound is directly combined with the under layer by chemical bonding. Accordingly, the precursor has the advantage that it is excellent in printing durability even when the image recording layer is thin.
Furthermore, in the lithographic printing plate precursor of the invention, it is preferred that a surface of the under layer with which the polymer compound is directly combined is roughened. By giving irregularities to the under layer surface (solid surface) as described later, the lithographic printing plate precursor of the invention has the features that the hydrophilicity of non-image areas is high, that the degree of discrimination between the hydrophilicity and the lipophilicity is increased, and that the scumming resistance in printing is excellent.